pentobarbital will reduce the level or effect of fosaprepitant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/observe. Doxycycline: Phenobarbital has been shown to shorten the 50 percent-lifetime of doxycycline for as long as 2 months right after barbiturate therapy is discontinued. pentobarbital will lessen the level or re